DOC: Add CONTRIBUTING.md file

Author: CavRiley

CONTRIBUTING.md

@@ -0,0 +1,73 @@
+# Contributing to ITKPythonPackage
+
+## Getting Started
+
+Clone the repository and install the pre-commit hooks:
+
+```bash
+git clone https://github.com/InsightSoftwareConsortium/ITKPythonPackage.git
+cd ITKPythonPackage
+````
+
+Install [Pixi](https://pixi.sh) for managing the build environment:
+
+```bash
+curl -fsSL https://pixi.sh/install.sh | bash
+pixi install
+```
+
+Install pre-commit hooks
+
+```bash
+pixi run pre-commit-install
+# optionally run pre-commit hooks
+pixi run pre-commit-run
+```
+
+
+## Development Workflow
+
+### Code Style
+
+Pre-commit hooks enforce all formatting and linting automatically on commit:
+
+- **Python**: Black (formatting), Ruff (linting + import sorting)
+- **Shell**: ShellCheck (linting), shfmt (formatting)
+- **TOML**: Taplo (formatting)
+
+Run against all files manually:
+
+```bash
+pre-commit run --all-files
+```
+
+### Commit Messages
+
+This project uses [Conventional Commits](https://www.conventionalcommits.org), enforced by Commitizen:
+
+```
+feat: add support for Python 3.12 wheels
+fix: correct cmake args not propagating to module builds
+chore: update pre-commit hook versions
+docs: clarify aarch64 build requirements
+```
+
+Commitizen will reject commits that don't follow this format.
+
+### Building Docs
+
+```bash
+pip install -r docs/requirements-docs.txt
+sphinx-build -W -b html docs docs/_build/html
+```
+
+## Submitting a Pull Request
+
+1. Create a branch from `main`
+2. Make your changes and ensure `pre-commit run --all-files` passes
+3. Open a PR, fill out the template, including which platforms you tested on
+4. CI will run pre-commit checks automatically
+
+## Questions
+
+For build questions or general ITK support, use the [ITK Discourse forum](https://discourse.itk.org).